1. Field of the Invention
The present invention relates in general to carbon coatings, and in particular to a low cost carbon fiber-coating produced via a precursor/solvent solution and the methods and processes for fabricating such a carbon fiber-coating.
2. Related Art
Tailored-conductivity fiber coatings are useful for many applications such as electromagnetic interference/radio frequency interference (EMI/RFI) shielding, static dissipation materials, and conductivity-tailoring of fiber-reinforcement for low observable applications. For lower temperature applications, such as tailored conductivity shielding applications, carbon is a very desirable fiber coating because of the relative ease of application, via chemical vapor deposition (CVD), and its availability. Also, carbon is a very desirable conductive coating because of its availability, resistance to environmental degradation, and low toxicity.
Also, interfacial coatings are very desirable for use with ceramic matrix composites (CMC's). For example, CMC's are useful for many applications because they possess high-temperature mechanical performance and exhibit a high strain-to-failure compared to monolithic ceramics. In order to achieve high strains-to-failure, many CMC systems require the interfacial coating between the fibrous reinforcement material and the ceramic matrix. The interfacial coating provides a weak bond between the fiber and matrix that allows fiber "pullout" (ductile shear movement instead of brittle fracture) during tensile stress application. In other words, the interfacial coating creates a weak disbond layer between the ceramic matrix and fibers, thereby imparting desired ductile qualities to the final CMC.
However, parts or fabrics that are coated via CVD, sputtering, or evaporation are limited in size to the internal capacity of the CVD furnace or sputtering/evaporation chamber. Also, coating uniformity is usually difficult to achieve due to line-of-sight masking during coating application. In addition, current methods for application of conductive coatings onto normally non-conductive fibers (for example, oxide ceramic fibers, such as Nextel, or fiberglass fibers) is often expensive and/or complex, such as sputtering or chemical vapor deposition (CVD). Further, the materials used for conductive coatings are often hazardous (such as chrome-silicide and titanium silicide), degrade via oxidation or moisture attack (such as nickel-based coatings), or are exorbitantly expensive (such as gold coatings).
As a result, the excess cost of the application techniques or inability to apply uniform coatings prevents the use of CMC's or conductive carbon coatings in low-cost, high volume applications, such as for the production of parts for the automotive industry or tailored-conductivity EMI/RFI shielding applications.
Therefore, what is needed is a low cost carbon coating application process capable of enabling tailored-conductivity fabric materials and/or CMC materials to compete effectively against other low-cost materials. What is also needed is a method to apply low-cost carbon coatings with inexpensive raw materials, low labor involvement, part size limited only by the capacity of the pyrolysis furnace, and improved coating uniformity.
Whatever the merits of the above mentioned systems and methods, they do not achieve the benefits of the present invention.